forest ecology

Ecology Practical Manual (MSc II): Forest Ecology
1. Comparison of species diversity between different forests
Species diversity is the combination of species richness and species evenness. Species richness is the
number of individuals per unit area. Species evenness is the distribution of individuals among the species.
Evenness is maximum when all the species have same or nearly equal number of individuals. Species
diversity is often calculated for each stratum in a community rather than for the entire community.
Species diversity can be expressed in single index number. Among the several indices, most
commonly used two indices are Simpson's index (Simpson 1949) and Shannon-Wiener's index (Shannon
and Weaver 1949). Simpson's index (C) reflects dominance because it is more sensitive to the most
abundant species than the rare species. So the values do not vary significantly from sample to sample
because it is the rare species that varies from place to place more than the common ones. It is calculated as
follows:
s
C = ∑ (Pi)2 where, C = Simpson' index of dominance
i =1 s = total number of species
Pi=proportion of all individuals in the sample that belongs to species i
Shannon-Wiener Index (H') is calculated as follows
s
H' = - ∑ (Pi) (ln Pi)
i =1
Values of H' varies from 0 for a community of one species, to 7 or more in rich forest, it is >3 for
deciduous forest of eastern US, 3.59 for sal forest of eastern Himalayan low land (Shankar 2001), 2.49 to
3.8 for sal forest of lower Arun river basin, eastern Nepal (Duwadee 2002), 1.06-1.30 for community
managed sal forests of mid hill, central Nepal (Shrestha 2003).
Fig. 1 Comparison of diversity indices (Simpson and Shannon-Wiener indices) between Namjung and
Khari forest
Species Namjung forest Khari forest
code No. per Pi Pi2 Pi ln Pi No. per Pi Pi2 Pi ln Pi
ha ha
1 909 0.740 0.5476 0.222 125 0.498 0.248004 0.347
2 108 0.088 0.007744 0.213 84 0.334 0.111556 0.366
3 67 0.054 0.002916 0.157 6 0.024 0.000576 0.089
4 25 0.020 0.0004 0.078 12 0.048 0.002304 0.145
5 17 0.013 0.000169 0.056 6 0.024 0.000576 0.089
6 17 0.013 0.000169 0.056 6 0.024 0.000576 0.089
7 17 0.013 0.000169 0.056 6 0.024 0.000576 0.089
8 17 0.013 0.000169 0.056 6 0.024 0.000576 0.089
9 17 0.013 0.000169 0.056
10 17 0.013 0.000169 0.056
11 8 0.006 0.000036 0.030
12 8 0.006 0.000036 0.030
Total 1227 C=0.5597 H'=1.066 251 C=0.3647 H'=1.30
(∑)
Total number of species (species richness) is higher in Namjung forest than in Khari, but species diversity
is higher in later. Despite higher species richness in Namjung forest, contribution of single dominant
species is very high and other species are rare. It reduced the species diversity (H'). Namjung forest has
higher Simpson's index because the index is more sensitive to dominant species. In Khari forest the number
of common species is higher which increases the species diversity (H').
1 BBS/CDB/TU/04
Ecology Practical Manual (MSc II): Forest Ecology
Exercise: Calculate species diversity of community (protected) and national (non protected) forests and
discuss your results. Both forest are dominated by Shorea robusta.
Tree density (pl/ha)
SN Community Forest National Forest
1 1.06 1.06
2 2.12 1.06
3 15.9 1.06
4 1.6 1.06
5 15.9 1.06
6 1.06 7.42
7 2.12 1.06
8 1.06 8.48
9 11.66 6.36
10 9.58 1.06
11 12.7 3.18
12 6.36 1.06
13 5.32 2.12
14 1.6 3.18
15 2.12 19.09
16 9.54 153.78
17 8.84 2.12
18 50.9 2.12
19 3.18 2.12
20 13.78 2.12
21 1.06 2.12
22 42.42 3.18
23 11.66 1.06
24 1.06 -
25 3.18 -
2 BBS/CDB/TU/04